Quiz 7-solutions - Version 027 Quiz 7 fakhreddine(51615...

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Version 027 – Quiz 7 – fakhreddine – (51615) 1 This print-out should have 5 questions. Multiple-choice questions may continue on the next column or page – Fnd all choices before answering. 001 2.0 points THINK!!! No need to do any calculation! Which of the following indicators would be the best choice to determine the end point of a titration of 0.100 M HCl with a solution of the weak base CH 3 NH 2 ? 1. thymolphthalein, k in = 1 . 3 × 10 - 10 2. litmus, k in = 1 × 10 - 7 3. methyl orange, k in = 2 × 10 - 4 correct Explanation: The endpoint of a weak base - strong acid (HCl) titration is below pH 7, corresponding to the p K a of methyl orange. 002 2.0 points 50 mL of 2 . 0 M acetic acid (CH 3 COOH) was titrated with 1 . 0 M NaOH. What is the pH at the equivalence point of this titration? The ionization constant is 1 . 8 × 10 - 5 . 1. 10.52 2. 7.00 3. 9.20 4. 9.28 correct 5. 9.52 Explanation: [CH 3 COOH] = 2.0 M [NaOH] = 1.0 M V CH 3 COOH = 50 mL K a = 1 . 8 × 10 - 5 Initially, [CH 3 COOH] = (50 mL)(2.0 M) = 100 mmol CH 3 COOH+NaOH Na + +CH 3 COO - + H 2 O ini 100 100 0 0 Δ 100 100 100 100 Fn 0 0 100 100 Na + is a spectator ion.
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Quiz 7-solutions - Version 027 Quiz 7 fakhreddine(51615...

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